In recent years, research has been conducted on heat-assisted magnetic recording technology which achieves high-density recording by a combination of optical technology and magnetic recording/reproducing technology. The heat-assisted magnetic recording technology is used in a magnetic recording/reproducing apparatus having heat means, a recording head, a reproducing head, and a magnetic recording medium. The following is a brief description of the operation of such a magnetic recording/reproducing apparatus. At a time of recording, first, in order to decrease coercivity of an area onto which data should be recorded (“recording area”) in the magnetic recording medium of the magnetic recording/reproducing apparatus, the temperature of the recording area is increased using the heat means (e.g., by applying laser light), and then, information is magnetically recorded onto the magnetic recording medium in such a way that an external magnetic field is applied to the recording area using the recording head. That is, heat-assisted magnetic recording is conducted. Meanwhile, at a time of reproduction, first, an area of the magnetic recording medium, which is subjected to reproduction (“reproduction area”) is heated using the heat means (e.g., by applying laser light), so that the temperature of the heated area is shifted from a compensation temperature and saturation magnetization is increased. Then, information is read out by the reproducing head.
Here is provided a brief description of the principle of heat-assisted magnetic recording. First, a graph in FIG. 16 shows an example of the relation among coercivity Hc, magnetization M, and temperature T, of a recording layer of a magnetic recording medium used in the above-described heat-assisted magnetic recording/reproducing apparatus. The recording layer having the property as illustrated in FIG. 16 shows extremely high coercivity Hc at or around room temperature (temperature E to temperature G), and therefore magnetic recording is difficult using a magnetic field generated by a typical recording head. However, such a recording layer is advantageous in that: its extremely high magnetic stability does not allow a weak magnetic field to erase information once recorded; and its high magnetization realizes high output by the reproducing head. Note that, however, as the temperature of the magnetic recording medium increases, the coercivity Hc of the magnetic recording medium decreases, and reaches approximately zero at its Curie point (Tc). Therefore, heating of the magnetic recording medium to raise the temperature thereof to temperature H, a temperature near the Curie point, allows recording to be conducted with a magnetic field used in a typical magnetic recording/reproducing apparatus. The Curie point varies depending on a material used as a magnetic layer or its composition, and ranges from 100° C. to 250° C., approximately. Thus, the stability of recorded information is ensured by conducting heat-assisted magnetic recording with the use of a magnetic recording medium including a magnetic layer higher in coercivity than that of a magnetic recording medium used in a typical recording method. The below-mentioned patent document 1 discloses this kind of heat-assisted magnetic recording technology.
Patent document 1: Japanese Unexamined Patent Publication No. 85702/2003 (Tokukai 2003-85702)